The half-year onslaught was part of a $20 million push by AFP. The group's biggest backers are the billionaire Koch brothers, and North Carolina mega-donor Art Pope served as its chair until he was appointed state budget director.

The ad campaign has been notable not only for its size and price tag, but also for its early entry into the 2014 political spending wars, launching 18 months before Election Day.

It's also helped cement North Carolina's status as one of the country's preeminent battleground states. Sen. Hagan has been far and away the biggest target of AFP's efforts: According to a New York Times analysis, the 3,535 spots going after Hagan account for 45 percent of the campaign's national total.

The ads seem to be having an impact. As the North Carolina-based firm Public Policy Polling reported on Jan. 14:

Hagan's main issue is that with independents she has a 30/56 approval rating and trails all of her opponents by double digits. Unpopularity of the Affordable Care Act seems to be driving much of her trouble. Only 38% of voters in the state overall support it to 48% who are opposed, and independents are more against it than the overall electorate at 31/57. 61% of voters think its implementation has been unsuccessful to 32% who deem it a success.

Democrats have struggled to catch up with the attack ad deluge. While AFP's spending on the Hagan ads in North Carolina is estimated at around $5 million, Democrats have reportedly answered with only $1.5 million worth of ads defending Hagan. In Louisiana, AFP has spent around $1.8 million compared to $625,000 in support of the Democrat.

But Democrats and their allies are using the AFP assault as a talking point in fundraising for more ads of their own. As Guy Cecil of the Democratic Senatorial Campaign Committee told the Times:

Democrats need money at this early stage in order to fight back against the limitless spending from the Kochs. As we get closer to the election, we will have the resources to introduce their Tea Party candidates before they have an opportunity to define themselves for voters, but right now the limitless spending from the Kochs means we need Democratic donors to step up in a bigger way immediately.